“The Germany-based laser and machine tool behemoth Trumpf announced that—working with scientists at the University of Geneva, Switzerland, and other organizations—it has hauled a 5-ton, 9-m-long “super laser” to the top of Säntis mountain in the Swiss Alps, and has installed and fired up the terawatt-scale light source. The ultimate goal of this audacious exercise: Demonstrate the ability of lasers to control and safely redirect lightning strikes…”
“Installé depuis le 18 mai au sommet du Säntis, dans les cantons d’Appenzell et St-Gall, un laser haute puissance vise à déclencher des éclairs et à guider la foudre loin des zones sensibles. Ce projet, intitulé «Laser Lightning Rod», est mené par un consortium européen dans lequel l’UNIGE a un rôle central. Des membres de la Section de physique de l’UNIGE ont participé au développement ainsi qu’au montage de la structure extérieure de l’expérience, dont certains éléments ont été installés par hélicoptère. Cet équipement est actuellement en phase de préparation pour pouvoir faire une campagne de mesures de juin à septembre, durant la haute saison des orages. Les chercheurs et chercheuses dirigeront le laser vers les orages et évalueront sa capacité à guider la foudre par le réchauffement et l’ionisation de l’air local.”
Many sensitive sites, such as nuclear power plants, power stations and other critical infrastructure may have insufficient lightning pro- tection and their electronic systems suffer damages due to direct or nearby lightning strikes. Similarly, thunderstorms paralyze airports every year, causing delays and requiring flights to be rerouted. A European consortium now plans to investigate and develop a new type of lightning protection using a high-power laser that will create ionized channels in the atmosphere and redirect lightning away from sensitive areas. The laser will be installed on the summit of the Säntis in the canton of Appenzell (Switzerland) and it will enter a test phase from June to September, during the peak thunderstorm season. On May 18, 2021, important elements of the experiment will be installed by helicopter. The École polytechnique (Paris, France), the University of Geneva (UNIGE, Switzerland), TRUMPF Scientific Lasers (Munich, Germany), André Mysyrowicz Consulting (AMC, France), the EPFL (Switzerland), the Haute école d’ingéniérie et de gestion du canton de Vaud – HEIG-VD (Switzerland) have joined forces to set up this European consortium.
T. Produit, T. Produit, P. Walch, C. Herkommer, A. Mostajabi, M. Moret, U. Andral, A. Sunjerga, M. Azadifar, Y.-B. André, B. Mahieu, W. Haas, B. Esmiller, G. Fournier, P. Krötz, T. Metzger, K. Michel, A. Mysyrowicz, M. Rubinstein, F. Rachidi, J. Kasparian, J.-P. Wolf, A. Houard, “The Laser Lightning Rod project,” The European Physical Journal, Applied Physics 92, 30501 (2020) http://dx.doi.org/10.1051/epjap/2020200243
Lightning is highly destructive due to its high power density and unpredictable character. Directing lightning away would allow to protect sensitive sites from its direct and indirect impacts (electromagnetic perturbations). Up to now, lasers have been unable to guide lightning efficiently since they were not offering simultaneously terawatt peak powers and kHz repetition rates. In the framework of the Laser Lightning Rod project, we develop a laser system for lightning control, with J-range pulses of 1 ps duration at 1 kHz. The project aims at investigating its propagation in the multiple filamentation regime and its ability to control high-voltage discharges. In particular, a field campaign at the Säntis mountain will assess the laser ability to trigger upward lightning.
(a) Principle of the general layout of the laser experiment implementation at Säntis (not to scale). (b) Schematic drawing of the sending telescope.
Installation of the LLR laser on Orsay for the filamentation campaign
Installation of the laser for the Laser Lightning Rod Project (llr-fet.eu) in Orsay for the first experiments on the characterization of the filaments. The laser delivers pulses of 700 mJ, 1 ps at 1 kHz (Photo @Pierre Walch, LOA)
Machine Learning-Based Lightning Localization Algorithm Using Lightning-Induced Voltages on Transmission Lines
H. Karami; A. Mostajabi; M. Azadifar; M. Rubinstein; C. Zhuang et al. “Machine Learning-Based Lightning Localization Algorithm Using Lightning-Induced Voltages on Transmission Lines,” IEEE Transactions on Electromagnetic Compatibility. 2020. Vol. 62, num. 6, p. 2512-2519. https://doi.org/10.1109/TEMC.2020.2978429
In this article, we present a machine learning-based method to locate lightning flashes using calculations of lightning-induced voltages on a transmission line. The proposed approach takes advantage of the preinstalled voltage measurement systems on power transmission lines to get the data. Hence, it does not require the installation of additional sensors such as extremely low frequency, very low frequency, or very high frequency. The proposed model is shown to yield reasonable accuracy in estimating two-dimensional geolocations for lightning strike points for different grid sizes up to 100 × 100 km 2 . The algorithm is shown to be robust against the distance between the voltage sensors, lightning peak current, lightning current rise time, and signal to noise ratio of the input signals.
Ultrafast thin-disk multipass amplifier with 720 mJ operating at kilohertz repetition rate for applications in atmospheric research
C. Herkommer, P. Krötz, R. Jung, S. Klingebiel, C. Wandt, R. Bessing, P. Walch, T. Produit, K. Michel, D. Bauer, R. Kienberger, and T. Metzger, “Ultrafast thin-disk multipass amplifier with 720 mJ operating at kilohertz repetition rate for applications in atmospheric research,” Optics Express 28, 30164 (2020) https://doi.org/10.1364/OE.404185
We present an ultrafast thin-disk based multipass amplifier operating at a wavelength of 1030 nm, designed for atmospheric research in the framework of the Laser Lightning Rod project. The CPA system delivers a pulse energy of 720 mJ and a pulse duration of 920 fs at a repetition rate of 1 kHz. The 240 mJ seed pulses generated by a regenerative amplifier are amplified to the final energy in a multipass amplifier via four industrial thin-disk laser heads. The beam quality factor remains ∼ 2.1 at the output. First results on horizontal long-range filament generation are presented.
Measurement and Modeling of Both Distant and Close Electric Fields of an M-Component in Rocket-Triggered Lightning
Q. Li; F. Rachidi; M. Rubinstein; J. Wang; L. Cai et al. “Measurement and Modeling of Both Distant and Close Electric Fields of an M-Component in Rocket-Triggered Lightning,” Journal of Geophysical Research: Atmospheres. 2020. Vol. 125, num. 21. https://doi.org/10.1029/2019JD032300
Simultaneous measurements of current and multiple-station electric fields associated with a 5.4-kA-peak M-component in rocket-triggered lightning are presented in this study. A close-range electric field measurement site was located northeast of the triggering site, 195° clockwise from South, at a distance of 78 m, while the distant multiple stations in this study were located southwest of the lightning triggering site (25–48°, clockwise from South) at a distance ranging from 69 to 126 km. Both the fast microsecond-scale and slow millisecond-scale pulses were observed at six distant stations. At the close station, the fast pulse was not noticeable. The magnitude and half-peak width of the fast pulse were in the range of 0.91–1.93 V/m and 2.0–3.0 μs, respectively. The corresponding parameters for the slow pulse were, respectively, in the range of 0.59–1.29 V/m and 20.0–25.1 μs. The time lag between the onset of the channel-base current and the far electric field of the M-component was 18 μs. This time lag was used to deduce the ratio of the M-component channel length and the wave speed. The classical guided wave M-component model proposed by Rakov et al. (1995, https://doi.org/10.1029/95JD01924) to simulate the slow, millisecond-scale field pulse assumes that neither the incident nor the reflected current wave undergoes attenuation even though the wave propagation occurs along a lossy channel. A modified guided wave M-component model is proposed in this study in which the M-component current wave attenuates with an exponential decay. Based on the best agreement achieved between the simulated fields using the modified two-wave M-component model and the observed near and far electric fields, the channel length, the M-component wave speed, and the current attenuation constant were inferred, respectively, as 1.8 km, 1 × 108 m/s, and 3 km. It is shown that the modified guided wave M-component model is able to reproduce reasonably well the electric fields both at close and far distance ranges.
Dynamics of the femtosecond laser-triggered spark gap
E. W Rosenthal, I. Larkin, A. Goffin, T. Produit, M. C. Schoeder, J.-P. Wolf and H. M. Milchberg, “Dynamics of the femtosecond laser-triggered spark gap,” Optics Express 28, 24599 (2020) https://doi.org/10.1364/OE.398836
We present space and time resolved measurements of the air hydrodynamics induced by femtosecond laser pulse excitation of the air gap between two electrodes at high potential difference. We explore both plasma-based and plasma-free gap excitation. The former uses the plasma left in the wake of femtosecond filamentation, while the latter exploits air heating by multiple-pulse resonant excitation of quantum molecular wavepackets. We find that the cumulative electrode-driven air density depression channel plays the dominant role in the gap evolution leading to breakdown. Femtosecond laser heating serves mainly to initiate the depression channel; the presence of filament plasma only augments the early heating.